For an internal combustion engine to function reliably and according to the ideal parameters specified by its designers, it is necessary for its internal components to have high durability even under the most critical operating conditions. Accordingly, components such as piston rings and bearings, among others, must display resistance and durability against wear resulting from constant sliding, high temperatures and chemical and abrasive attack by products originating from the combustion that takes place inside the cylinders.
In view of this high durability that is required, sliding components such as piston rings and bearings are given coatings to better withstand the endless operating cycles of the engines, and the coatings applied to these components are constantly being refined, with as premises the base material of which the component is composed, the operating parameters of the engine, the costs of manufacture, etc.
Specifically with respect to piston rings, some coatings have been developed for endowing these components with high durability at an advantageous cost of production.
A first coating is disclosed in the case of patent DE 10 2009 046 281, which relates to a piston ring manufactured in steel or cast iron that has a coating consisting of a DLC layer without metal or composed of a metallic inner layer and a nonmetallic top layer, a layer of chromium nitride (CrN) deposited by the PVD process (physical vapor deposition) and a ceramic Me (CxNy) intermediate layer.
The nitrided layer is applied on the ring base and the aforementioned intermediate layer is applied thereon subsequently. Finally, the coating DLC is applied on the intermediate layer.
Optionally (non-obligatory), an adhesive layer is provided, which forms the bond between the layer of chromium nitride applied by PVD and the base of the piston ring or the like.
A vulnerability of this coating is that the Me(CxNy) bonding layer is fragile and brittle, and can result in premature detachment of the covering, resulting in a shorter service life of the internal combustion engine, which is undesirable in terms of marketing.
Moreover, in contrast to the coating now proposed, this coating of the prior art does not possess a transition layer consisting of tungsten carbide WC1-x.
Document DE 10 2008 042 747 discloses a sliding component such as a piston ring, the coating of which comprises an adhesive layer consisting of metallic chromium applied on the substrate, a nitrided layer (CrN) applied by the PVD process (physical vapor deposition), an inner layer provided with carbon that possesses greater hardness and/or contains a small percentage of hydrogen than an outer layer provided with carbon preferably of the type a-C:H.
The disadvantage of this second coating is that hydrogen promotes formation of the sp3 electronic structure (the same structure as diamond) and with reduction of this there will be an increase in sp2 structure (the same structure as graphite). As a result, the wear resistance of this covering is compromised.
Moreover, as a difference relative to the coating now developed, this coating of the prior art has, as a large difference, the second layer, counting from outside inwards, which has the form of amorphous carbon contrary to the innovative multilayer structure (W—C:H) and (a-C:H). Accordingly, the performance indices achieved by this coating are lower, notably in resistance to crack propagation.
Document DE 10 2009 028 504, in its turn, discloses a piston ring manufactured in steel or cast iron covered initially with an adhesive layer, to which an intermediate layer is applied containing carbon and a metal, especially tungsten and a layer of DLC without a metallic component. The average thickness of this coating is from 5 μm to 40 μm, the ratio of the thickness of the outer layer to that of the intermediate layer is from 0.7 to 1.5 and the ratio of the thickness of the outer layer to the total thickness of the coating is from about 0.4 to 0.6.
As a large difference relative to the coating now developed, this prior art does not have an intermediate layer configured as a (W—C:H) and (a-C:H) multilayer structure. In fact, this layer is absent from this coating and, accordingly, the performance indices achieved with it are lower, notably in resistance to crack propagation.
Finally, document US 2007/0078067 discloses a coating applied to at least one sliding part, characterized in that it comprises a film of amorphous carbon on the sliding surface of the component and has a ratio of total intensity in the Raman spectrum of band D (associated with carbon disorder sp2) to band G (monocrystalline graphite) between 1.5 and 2.0.
The coatings discussed above have properties that make them unsatisfactory for use in engine components, since they do not simultaneously display high wear resistance and durability suitable for operation within an internal combustion engine. The applicant has developed another coating, novel and inventive compared to the others, that offers significant advantages such as ease of deposition, excellent mechanical properties and competitive cost of application, high wear resistance and toughness compatible with the requirements of modern engines. The present coating can be applied to any sliding components used in an internal combustion engine such as piston rings, bearings, bushes, sleeves, etc., even though they are iron-based.